Shoe bottoms and shoes

ABSTRACT

When a midfoot portion of a sole is divided by a predetermined sole center line into a medial midfoot region and a lateral midfoot region one on each side in the foot width direction, a rigidity lowering portion, which is provided in the medial midfoot region, is provided and, in such a manner that the bending rigidity of the medial midfoot region around a foot width direction axis becomes smaller than that of the lateral midfoot region, the rigidity lowering portion in the medial midfoot region reduces the bending rigidity of the medial midfoot region due to another factor other than the shape of the medial edge and the shape of the lateral edge of the sole in a planar view.

TECHNICAL FIELD

The present invention relates to shoe bottoms of shoes.

BACKGROUND ART

In the related art, attempts have been made for providing variousfunctions to shoes by devising soles of shoe bottoms (e.g., see PatentDocument 1).

[Patent Document 1] International Publication No. 2017/046959

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

When doing a front bridge motion or the like during core training, awearer of shoes (hereinafter simply referred to as a wearer) may take astanding on tiptoe posture. The expression “standing on tiptoe posture”in the present specification means a posture in which at least arearfoot portion of the sole is lifted from the ground under thecondition that a forefoot portion of the sole described later is incontact with the ground. There is no particular limitation on the anglethat the sole makes with the ground at parts other than the part incontact with the ground.

If the muscular strength of the wearer's legs is weak, it tends to bedifficult to stably maintain the standing on tiptoe posture. From theviewpoint of supporting the exercise of the wearer, it is desirable topropose shoe bottoms that allow for good stability while taking astanding on tiptoe posture. As a result of study based on such aviewpoint, the inventors of the present invention have come to realizethat there is room for improvement in the shoe bottoms described inPatent Document 1, as described later in detail.

One embodiment of the present invention has been made in view of suchproblems, and one of the purposes of the invention is to provide shoebottoms that are capable of improving the stability of a standing ontiptoe posture.

Means to Solve the Problem

One embodiment of the present invention relates to a shoe bottom that isa shoe bottom comprising a sole, wherein when a midfoot portion of thesole is divided by a predetermined sole center line into a medialmidfoot region and a lateral midfoot region one on each side in the footwidth direction, the shoe bottom has a rigidity lowering portion that isprovided in the medial midfoot region, and wherein, in such a mannerthat the bending rigidity of the medial midfoot region around a footwidth direction axis becomes smaller than that of the lateral midfootregion, the rigidity lowering portion in the medial midfoot regionreduces the bending rigidity of the medial midfoot region due to anotherfactor other than the shape of the medial edge and the shape of thelateral edge of the sole in a planar view.

Advantage of the Invention

According to the present invention, shoe bottoms that are capable ofimproving the stability of a standing on tiptoe posture can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a sole that serves as one invention example;

FIG. 2 is a plan view showing the skeleton of a foot of a human body;

FIG. 3 are diagrams in which the skeleton of the right foot of a weareris viewed from the front side in the foot longitudinal direction; FIG.3A shows a positional relationship when the toes and heel of the wearerare in contact with the ground; FIG. 3B shows a state where a crossingangle is larger compared to the positional relationship of FIG. 3A;

FIG. 4 are diagrams showing the calcaneocuboid joint surface andtalonavicular joint surface of the right foot of the wearer;

FIG. 4A shows a positional relationship when the toes and heel of thewearer are in contact with the ground; FIG. 4B shows a state where acrossing angle is larger compared to the positional relationship of FIG.4A;

FIG. 5 are diagrams for explaining the axis of motion of a Chopartjoint; FIG. 5A is a plan view of the skeleton of the right foot; FIG. 5Bis a view of the skeleton thereof viewed from the medial side in thefoot width direction;

FIG. 6 is a bottom view showing another invention example of a soleprovided with rigidity lowering portions;

FIG. 7 is a bottom view of a sole that serves as still another inventionexample;

FIG. 8 is a perspective view schematically showing a model simulating asole used for analysis;

FIG. 9 is a diagram showing the result of the analysis;

FIG. 10 is a diagram for explaining an external torsional resistanceexpected region;

FIG. 11 is a diagram showing a sole according to a reference exampleused for the analysis;

FIG. 12 is a graph showing torsional frequencies obtained by theanalysis;

FIG. 13A is a diagram showing the measurement result for torsion anglesobtained by an experiment; FIG. 13B is a diagram showing the measurementresult for the amount of the ankle unstableness;

FIG. 14 is a bottom view of a sole according to a first exemplaryvariation;

FIG. 15 is a side view of a shoe using a shoe bottom according to afirst embodiment as viewed from the medial side in the foot widthdirection;

FIG. 16 is a bottom view of a sole according to the first embodiment;

FIG. 17 is a bottom view of a sole according to a second embodiment;

FIG. 18A is a side view of the sole according to the second embodimentas viewed from the medial side in the foot width direction; FIG. 18B isa side view of the sole viewed from the lateral side in the foot widthdirection;

FIG. 19A is a bottom view of a sole according to a second exemplaryvariation; FIG. 19B is a bottom view of a sole according to a thirdexemplary variation; FIG. 19C is a bottom view of a sole according to afourth exemplary variation;

FIG. 20 is a side view of a shoe bottom according to a third embodimentas viewed from the same viewpoint as that of FIG. 15; and

FIG. 21 is a side view of a shoe bottom according to a fourth embodimentas viewed from the same viewpoint as that of FIG. 15.

MODE FOR CARRYING OUT THE INVENTION

Terms used in this specification will be explained. FIG. 1 is a planview showing a sole 10, which serves as one invention example. A “footlongitudinal direction Lx” in the present specification means adirection along a straight line connecting a tip 10 a on the toe sideand an end 10 b on the heel side of the sole 10. The toe side in thefoot longitudinal direction Lx is also referred to as the front side,and the heel side is also referred to as the back side. A “foot widthdirection Y” refers to a horizontal direction orthogonal to the footlongitudinal direction Lx. A first toe side of the foot of a wearersupported by the sole 10 is referred to as the medial side, and a fifthtoe side is referred to as the lateral side. A “full length La” in thefoot longitudinal direction Lx is the longest length in the footlongitudinal direction Lx, and a “full width Lb” in a foot widthdirection Ly is the longest length in the foot width direction Ly.

FIG. 2 is a plan view showing the skeleton of a foot of a human body.The foot of a human body is mainly composed of cuneiform bones Ba, acuboid bone Bb, a navicular bone Bc, a talus Bd, a calcaneus Be,metatarsal bones Bf, and phalanges Bg. The joint of the foot includes anMP joint Ja, a Lisfranc joint Jb, and a Chopart joint Jc. The Chopartjoint Jc includes a calcaneocuboid joint Jc1 formed by the cuboid boneBb and the calcaneus Be and a talonavicular joint Jc2 formed by thenavicular bone Bc and the talus Bd. A “midfoot portion” of a wearer(hereinafter, simply referred to as a human midfoot portion) in thepresent specification means the portion from the MP joint Ja to theChopart joint Jc.

FIG. 1 is referred back. A straight line along the foot width directionY, which is assumed to pass the heel side end of the MP joint Ja of thewearer, is defined as a line p. A straight line along the foot widthdirection Y, which is assumed to pass the toe side end of the Chopardjoint Jc of the wearer, is defined as a line q. The line p and the lineq are, for example, straight lines along the foot width direction Y thatdivide the full length La of the sole 10 in the foot longitudinaldirection Lx into 1.5:1.0:1.1 from the toe side to the heel side. A“forefoot portion 12” of the sole 10 in the present specification meansa region on the toe side of the line p, a “midfoot portion 14”(hereinafter simply referred to as a sole midfoot portion 14) of thesole 10 means a region from the line p to the line q, and a “rearfootportion 16” of the sole 10 means a region on the heel side of the lineq. The sole midfoot portion 14 can be also considered to be a regionthat is assumed to overlap with the range from the heel side end of theMP joint Ja to the toe side end of the Chopard joint Jc of the wearer,that is, a range that is assumed to overlap with the human midfootportion.

The background for how the shoe bottom according to the presentembodiment has been conceived of will be explained. As described above,if the muscular strength of the wearer's legs is weak, it tends to bedifficult to stably maintain the standing on tiptoe posture. Further, ifthe muscular strength of the wearer's legs is weak, a decrease inpropulsive force in a pushing-off motion during the terminal stance of agait cycle is known as a factor for falling down. This wearer is, forexample, a woman, an elderly person, or the like.

From the viewpoint of solving these problems, the inventors of thepresent invention found out, based on the anatomical viewpoint of thefoot of the human body, that it was effective to induce a bony lockingmechanism in the human midfoot portion of the wearer.

FIGS. 3 and 4 are diagrams in which the skeleton of a right foot of thewearer is viewed from the front side in the foot longitudinal directionLx. FIG. 3 are external views of the skeleton, and FIG. 4 are diagramsshowing a calcaneocuboid joint surface Sja and a talonavicular jointsurface Sjb of the right foot. FIGS. 3A and 4A show a positionalrelationship when the toes and heel of the wearer are in contact withthe ground, and FIGS. 3B and 4B show a state where a crossing angle θcdescribed later is larger compared to the positional relationship ofFIGS. 3A and 4A, respectively. The crossing angle between a joint axisAj1 of the calcaneocuboid joint Jc1 of the Chopart joint Jc viewed fromthe front in the foot longitudinal direction Lx and a joint axis Aj2 ofthe talonavicular joint Jc2 is defined to be θc.

FIG. 5 area diagram for explaining the axis of motion of the Chopartjoint Jc. FIG. 5A is a plan view of the skeleton of the right foot, andFIG. 5B is a view of the skeleton thereof viewed from the medial side inthe foot width direction. The Chopart joint Jc has a longitudinal axisand a clinoaxis as two axes of motion, of which the longitudinal axisserves as the joint axis Aj1 of the calcaneocuboid joint Jc1 and theclinoaxis serves as the joint axis Aj2 of the talonavicular joint Jc2.Although there are individual differences in terms of a skeleton, ingeneral, the calcaneocuboid joint Jc1 is an axis obtained by tilting thetoe side inward by 9 degrees in the foot width direction with respect tothe horizontal plane and tilting the toe side upward by 15 degrees withrespect to the sagittal plane, based on the state where the toe and theheel are in contact with the ground. Normally, the talonavicular jointJc2 is an axis obtained by tilting the toe side inward by 57 degrees inthe foot width direction with respect to the horizontal plane andtilting the toe side upward by 52 degrees with respect to the sagittalplane, based on the state where the toe and the heel are in contact withthe ground.

As shown in FIG. 3B, the bony locking mechanism is realized when thecrossing angle θc is increased to a certain extent compared to thatobtained when the wearer's toe and heel are in contact with the ground.Due to an increase in this crossing angle θc, the mobility of theChopart joint Jc is reduced compared with a case where the crossingangle θc is small, and the Chopart joint Jc can be turned into a rigidbody. This allows unstable between a plurality of bones constituting theChopart joint Jc to be prevented when taking a standing on tiptoeposture, and the stability of the standing on tiptoe posture can beimproved. Further, as a result of turning the Chopart joint Jc into arigid body, the propulsive force transmission between the plurality ofbones constituting the Chopart joint Jc becomes smooth, and thepropulsive force in the pushing-off motion can be improved.

The crossing angle θc of the plurality of joint axes forming the Chopartjoint Jc described above is known to increase as the amount of externaltorsion at the human midfoot portion increases. Therefore, in inducingthe bony locking mechanism, it is necessary to increase the amount ofexternal torsion at the human midfoot portion. The external torsionmeans that the heel is twisted in the supination direction with respectto the toes based on the positional relationship obtained when the toesand heel of the human body are in contact with the ground. The presentinventors have found that it is preferable to satisfy the followingcondition in order to achieve such an increase in the amount of externaltorsion at the human midfoot portion.

When the human midfoot portion is attempted to be twisted outward(external torsion), the sole 10 is also attempted to be twisted outwardin a range including the sole midfoot portion 14 following thedeformation of the human midfoot portion. Therefore, in order toincrease the amount of external torsion at the human midfoot portion, itis desirable to reduce the external torsional resistance of the sole 10within the range including the sole midfoot portion 14.

In order to respond to such a demand, the inventors of the presentinvention found out that it is effective to provide a rigidity loweringportion 32 for lowering the bending rigidity around a foot widthdirection axis (hereinafter, simply referred to as “bending rigidity”)in a medial midfoot region 20 of the sole midfoot portion 14, as shownin FIG. 1. The medial midfoot region 20 means a region located on themedial side when the sole midfoot portion 14 is divided into two regionsone on each side in the foot width direction by a predetermined solecenter line s. Of these two regions, the region located on the lateralside is referred to as a lateral midfoot region 22.

This sole center line s is defined as a line passing through the centerpart of the sole 10 in the foot width direction Y. In this example, astraight line along the foot longitudinal direction X that divides thefull width Lb of the sole 10 into 1.2:1.0 from the medial side to thelateral side in the foot width direction is defined as the sole centerline s. The sole center line s in this example is also a part on which afoot width direction center part of the foot of the wearer is assumed tobe located. The foot width direction center part is assumed to be a partlocated on a straight line passing through a third metatarsal bone Bf3and a medial process of calcaneal tuberosity Bel of the calcaneus Be ofa human body. FIG. 1 shows a range in which the medial process ofcalcaneal tuberosity Bel is assumed to be located.

Rigidity lowering portions 32 of the medial midfoot region 20 reduce thebending rigidity of the medial midfoot region 20 such that the bendingrigidity of the medial midfoot region 20 becomes smaller than that ofthe lateral midfoot region 22. The expression “the bending rigidity ofthe medial midfoot region 20 becomes smaller than that of the lateralmidfoot region 22” includes the following two cases. The first case is acase where, in the lateral midfoot region 22 and the medial midfootregion 20, only the bending rigidity of the medial midfoot region 20 isreduced. The second case is a case where, when reducing the bendingrigidity of both the lateral midfoot region 22 and the medial midfootregion 20, the amount of decrease in the bending rigidity in the medialmidfoot region 20 is set to be larger than that in the lateral midfootregion 22.

The rigidity lowering portions 32 in the medial midfoot region 20 reducethe bending rigidity of the medial midfoot region 20 due to anotherfactor other than the shape of a medial edge 10 c and the shape of alateral edge 10 d of the sole 10 in a planar view. This “another factor”is, for example, any one or a combination of two of recessed portionsthat are open on the ground contact surface of the sole 10 and theelongation characteristic of the material constituting the sole 10 suchas those explained in the following.

The expression “recessed portions that are open on the ground contactsurface of the sole 10” means those that are recessed upward from theground contact surface of the sole 10, which comes into contact with theroad surface. The recessed portions may be groove portions continuous inthe in-plane direction of a ground contact surface 10 e of the sole 10or may not be continuous in the in-plane direction thereof. FIG. 6 is abottom view showing another invention example of the sole 10 providedwith rigidity lowering portions 32. When the recessed portionsconstituting the rigidity lowering portion 32 are not continuous in thein-plane direction, the recessed portions may be provided intermittentlyso as to be aligned on a virtual line such as a straight line, a curvedline or the like. As the recessed portions, FIG. 1 shows medialtransverse groove portions 34 extending from the medial edge 10 c of thesole 10 in the foot width direction Y. When such recessed portions areprovided in the medial midfoot region 20, the bending rigidity of themedial midfoot region 20 can be lowered compared to that in a case wheresuch recessed portions do not exist. The bending rigidity of the medialmidfoot region 20 being reduced due to the recessed portions means sucha situation. When the recessed portions are the medial transverse grooveportions 34, the bending rigidity can be effectively reduced.

Further, the expression “the elongation characteristic of the materialconstituting the sole 10” means, specifically, the Young's modulus[N/mm²] in the foot longitudinal direction X of the materialconstituting the sole 10. The rigidity lowering portions 32 are formedusing a second material having a smaller Young's modulus in the footlongitudinal direction X than that of a first material constitutingportions adjacent to the rigidity lowering portions 32 of the sole 10.This allows the bending rigidity of the medial midfoot region 20 to belowered compared to a case where the rigidity lowering portions 32 areformed using the first material. The bending rigidity of the medialmidfoot region 20 being reduced due to the elongation characteristic ofthe material constituting the sole 10 means such a situation.

On the medial edge 10 c of the sole midfoot portion 14, a curved-in part10 f recessed outward in the foot width direction X is formed. Thebending rigidity of the medial midfoot region 20 of the sole 10 is oftensmaller than the bending rigidity of lateral midfoot region 22 due tothe influence of the curved-in part 10 f. In order to exclude theinfluence of this curved-in part 10 f, the shape of the medial edge 10 cand the lateral edge 10 d of the sole 10 in a planar view is excludedfrom the above-mentioned factors, which cause a decrease in bendingrigidity.

By providing such a rigidity lowering portion 32 in the medial midfootregion 20, it is easier to lower the bending rigidity of the medialmidfoot region 20 than that of the lateral midfoot region 22 as comparedwith the case where the rigidity lowering portion 32 is not provided. Asthe bending rigidity of the medial midfoot region 20 is lowered comparedto that of the lateral midfoot region 22, the elongation amount of themedial midfoot region 20 at the ground contact surface can be increasedcompared to that of the lateral midfoot region 22 when the sole 10 isbendingly deformed around the foot width direction axis. This means thatwhen the wearer is taking a standing on tiptoe posture, the medialmidfoot region 20 can be more easily deformed in an extended manner inthe foot longitudinal direction X than the lateral midfoot region 22,that is, the medial midfoot region 20 tends to be easily twistedoutward. In other words, it means that external torsional resistance atthe sole midfoot portion 14 can be lowered compared with the case wherea medial midfoot region 20 is not provided with a rigidity loweringportion 32. Therefore, by providing a rigidity lowering portion 32 inthe medial midfoot region 20, when the wearer attempts to twist his/herhuman midfoot portion while taking a standing on tiptoe posture, theamount of external torsion can be increased compared to the case where arigidity lowering portion 32 is not provided. As a result, it ispossible to induce the bony locking mechanism and thus improve thestability of the standing on tiptoe posture and improve the propulsiveforce in the pushing-off motion.

The medial midfoot region 20 is formed such that the bending rigiditythereof is smaller than that of the lateral midfoot region 22. This isrealized by providing a rigidity lowering portion 32 in the medialmidfoot region 20 or due to the shape of the medial edge 10 c or thelateral edge 10 d of the sole 10 in a planar view. These bendingrigidities may be evaluated based on the strain amount of the groundcontact surface in the foot longitudinal direction obtained when abending moment of a predetermined size around the foot width directionaxis is applied toward the upper surface of the sole at a toe side endportion and a heel side end portion of the midfoot region beingmentioned. It means that the bending rigidity becomes small as thisstrain amount increases. The bending rigidity of the medial midfootregion 20 being smaller than that of the lateral midfoot region 22 meansthat the strain amount in the medial midfoot region 20 is larger thanthe strain amount in the lateral midfoot region 22. The strain amountmay be acquired by actually cutting out the midfoot region beingmentioned from the sole 10 and measuring the strain amount using thepiece that has been cut out.

Further, as described above, the line q indicates a portion where theChopard joint of the foot of the wearer is assumed to be located. As arigidity lowering portion 32 is located closer to this line q, the solemidfoot portion 14 becomes more likely to be twisted outward at alocation closer to the Chopart joint Jc, and the bony locking mechanismis more likely to be induced accordingly. Therefore, the rigiditylowering portion 32 is preferably provided in a region on the heel sideof a straight line y along the foot width direction Y, which bisects thefull length of the sole midfoot portion 14 in the foot longitudinaldirection, in the medial midfoot region 20 of the sole midfoot portion14.

During the standing on tiptoe posture, a load for twisting the sole 10outward is applied to the sole 10 via the upper of the shoe in a statewhere the forefoot portion 12 of the sole 10 is restrained. At thistime, the toe side end portion of the sole midfoot portion 14 is fixed,and an external torsion load is applied to the heel side end portionthereof. At this time, the most deformed portion of the sole midfootportion 14 is a region on the toe side of the sole midfoot portion 14close to the forefoot portion 12 restrained in the sole 10. In thisregion on the toe side of the sole midfoot portion 14, it is possible toeffectively twist the sole midfoot portion 14 outward by havingdifferent bending rigidity on the medial side and the lateral side inthe foot width direction of the sole midfoot portion 14. Therefore, therigidity lowering portion 32 is also preferably provided in the regionon the toe side of the straight line y bisecting the sole midfootportion 14 in the foot width direction.

Next, another condition will be described that is preferably satisfiedin order to increase the amount of external torsion at the human midfootportion. A case is taken into consideration where an external torsionalload for twisting the sole 10 outward is applied to the sole 10 via theupper of the shoe when the wearer is taking a standing on tiptoeposture. A case is taken into consideration where a transverse grooveportion extending from the medial edge 10 c to the lateral edge 10 d isformed in the rearfoot portion 16 of the sole 10. In this case, evenwhen the external torsional load described above is applied to the sole10, the bending deformation at the transverse groove portion of therearfoot portion 16 thereof becomes dominant, and the amount of externaltorsion at the sole midfoot portion 14 becomes small. As a result, whenthe wearer attempts to twist his/her human midfoot portion outward whiletaking a standing on tiptoe posture, it is difficult to increase theamount of external torsion at the human midfoot portion due toresistance from parts other than the sole midfoot portion 14.

FIG. 7 is a bottom view showing a sole 10, which serves as anotherinvention example. In order to solve the above problems, as anothercondition, it is defined that a continuous surface 16 c continuous inthe foot longitudinal direction from a toe side end portion 16 a to aheel side end portion 16 b of a rearfoot portion 16 of the sole 10 isformed on the ground contact surface of the sole 10. In this figure, therange in which the continuous surface 16 c is formed is indicated byhatching with two-dot chain lines. This means that a transverse grooveportion extending from a medial edge 10 c to a lateral edge 10 d is notformed in the rearfoot portion 16 of the sole 10. In the illustratedexample, this continuous surface 16 c is formed in the entire range inthe foot width direction Y; however, the continuous surface 16 c may beformed in at least a part of the range in the foot width direction Y.

Thereby, when the wearer attempts to twist the midfoot portion outwardwhile taking a standing on tiptoe posture, the bending deformation ofthe sole 10 at the rearfoot portion 16 can be suppressed by thecontinuous surface 16 c, and a situation can be prevented where theamount of external torsion at the sole midfoot portion 14 becomes smallin accordance with the bending deformation. Accordingly, by satisfyingthe above-mentioned conditions, it becomes easier to obtain the effectof reducing the external torsional resistance at the sole midfootportion 14, and it thus becomes easier to increase the amount ofexternal torsion at the human midfoot portion.

When a reinforcing member such as a shank is attached to the solemidfoot portion 14, the bending rigidity of the shoe bottom becomesexcessively increased, and the external torsional resistance of the solemidfoot portion 14 thus becomes excessively increased. Therefore, in theshoe bottom according to the present embodiment, a reinforcing membersuch as a shank is preferably not attached to the sole midfoot portion14. This prevents an excessive increase in the bending rigidity of thesole midfoot portion 14 and allows the external torsional resistance ofthe sole midfoot portion 14 to be easily reduced.

The reinforcing member used in this case is those other than a midsole56 and an outer sole 58 of the sole 10 described later. This reinforcingmember is used, for example, for enhancing bending rigidity around thefoot width direction axis of the shoe bottom just like a shank or thelike and is formed using a material whose hardness is larger than themaximum hardness of the sole 10. This material is, for example, variousmetals or synthetic resins having a JIS A hardness of 80 degrees ormore. The JIS A hardness is a value obtained by measurement using an Atype hardness meter in compliance with JIS K 6301. The hardness of themidsole 56 is, for example, 35 to 75 degrees in terms of JIS C hardness,and the hardness of the outer sole 58 is, for example, 50 to 75 degreesin terms of JIS A hardness. The JIS C hardness is a value obtained bymeasurement using a C type hardness meter in compliance with JIS K 6301.

Even when the reinforcing member is not attached to the sole midfootportion 14, a reinforcing member may be attached to the sole forefootportion 12 and the sole rearfoot portion 16. Even under thisconfiguration, the external torsional resistance of the sole midfootportion 14 can be easily reduced.

Next, an analysis performed for coming up with the shoe bottom accordingto the embodiment will be explained. FIG. 8 is a perspective viewschematically showing a model simulating a sole 10 used for theanalysis. In this analysis, a sole having the same size as that of thesole 10 shown in FIG. 7 was used. The sole 10 had a full length La of280 mm, a full width Lb of 200 mm, and a uniform thickness of 20 mm. Thephysical conditions of the sole 10 were set to have a Young's modulus of6 [N/mm²], a Poisson's ratio of 0.25 [-], and a density of 3×10²[kg/m³]. It is assumed that this analysis reproduce the deformed stateof the sole 10 during a front bridge motion. For this reason, a regionSa in which the ball of foot of the toes of the wearer were assumed tohit was completely restrained, and an upward load Fz was applied to therearfoot portion 16 of the sole 10. In order to apply an externaltorsional load to the sole 10, a load Fy directed outward in the footwidth direction Y was applied to the rearfoot portion 16 of the sole 10.

FIG. 9 is a diagram showing the result of this analysis. In this figure,the distribution of the maximum principal stress at the bottom surfaceof the sole 10 obtained under the above-described conditions is shown.The higher the density of dots, the greater the stress. It can beconfirmed that when the external torsional load is applied to the sole10, the stress becomes larger in a region 24, which includes the medialmidfoot region 20 and the peripheral region of the sole 10, than thosein other regions. This means that this region 24 is strongly resistingthe external torsion of the sole midfoot portion 14. Therefore, it isconsidered that the external torsion at the sole midfoot portion 14 canbe effectively reduced by providing a rigidity lowering portion 32 inthe foregoing region 24 (hereinafter referred to as an externaltorsional resistance expected region 24), which is assumed to beresisting the external torsion of the sole midfoot portion 14.Therefore, as a region in which a rigidity lowering portion ispreferably provided, the external torsional resistance expected region24 obtained by this analysis is used.

FIG. 10 is a diagram for explaining the external torsional resistanceexpected region 24. The external torsional resistance expected region 24is geometrically specified in relation to the shape of the sole 10.Hereinafter, an explanation will be given with reference to thepositional relationship of the sole 10 in the planar view.

The definition of a line s, a line p, and a line q is the same as thedefinition described above. A straight line along the foot widthdirection Y that divides a region on the heel side of the line q of thesole 10 into 0.2:0.9 is defined as a line r. Being viewed from a pointo1, which is the intersection point of the line p and the line s, astraight line obtained by rotating the line p by 13 degrees around thepoint o1 in an outward direction Pa, which rotates the toe side outwardin the foot width direction, is defined as a line t. Being viewed fromthe point o1, which is the intersection point of the line s and the linep, a straight line obtained by rotating the toe side of the line s by 8degrees around the point o1 in the aforementioned outward direction Pais defined as a line u. Being viewed from a point o2, which is theintersection point of the line u and the line q, a straight lineobtained by rotating the line q by 5 degrees around the point o2 in theoutward direction Pa is defined as a line v. Being viewed from a pointP, which is the intersection point of the line r and the line u, astraight line obtained by rotating the liner by 4 degrees around thepoint P in the outward direction Pa is defined as a line w. A straightline connecting a point o5, which is the intersection point of themedial edge 10 c of the sole 10 and the line w, and the point o2 isdefined as a line x.

At this time, the external torsional resistance expected region 24 isdefined to be formed of a first region 26 surrounded by the line t, theline u, the line v, and the medial edge 10 c of the sole 10. Thisexternal torsional resistance expected region 24 is provided on theground contact surface of the sole 10 in the planar view of the sole 10.A rigidity lowering portion 32 is preferably provided in the foregoingexternal torsional resistance expected region 24. It is considered thatby providing the rigidity lowering portion 32 in this external torsionalresistance expected region 24, the external torsional resistance of thesole midfoot portion 14 can be effectively reduced.

The rigidity lowering portion 32 is preferably provided in apart (thepart indicated by a range S1) that belongs to the external torsionalresistance expected region 24 outside the medial midfoot region 20,other than the part that belongs to the external torsional resistanceexpected region 24 in the medial midfoot region 20. The rigiditylowering portion 32 provided in the part belonging to the externaltorsional resistance expected region 24 outside the range of the medialmidfoot region 20 also lowers the bending rigidity of the part due to arecessed portion that is open on the ground contact surface of the sole10, the elongation characteristic of the material constituting the sole10, and the like.

Referring to the analysis result of FIG. 9, the first region 26 definedas the external torsional resistance expected region 24 of the sole 10mainly spreads largely in a direction Lb heading toward the heel side ofthe foot longitudinal direction Lx. Further, the first region 26 alsospreads somewhat in a direction Lc heading toward the outside in thefoot width direction Y. This analysis is intended for a front bridgemotion. It is expected that a larger external torsional load will beapplied to the sole 10 in other motions such as running or the like. Ifa large load is applied to the sole 10, the external torsionalresistance expected region 24 is considered to first spread in thedirection Lb heading toward the heel side in the foot longitudinaldirection Lx. Further, the external torsional resistance expected region24 is considered to spread in the direction Lc heading toward theoutside in the foot width direction Y in an extent smaller than how theexternal torsional resistance expected region 24 spreads toward the heelside of the foot longitudinal direction Lx.

Therefore, as shown in FIG. 10, the external torsional resistanceexpected region 24 may be defined to be formed of the first region 26and a second region 28 surrounded by the line v, the line x, and themedial edge 10 c of the sole 10 in planar view. It is considered that byproviding the rigidity lowering portion 32 in the foregoing externaltorsional resistance expected region 24, the external torsionalresistance of the sole midfoot portion 14 can be effectively reducedwhen a large external torsional load is applied to the sole 10.

This rigidity lowering portion 32 is also preferably provided in parts(the range S1 and the part indicated by a range S2) that belong to theexternal torsional resistance expected region 24 outside the medialmidfoot region 20, other than the part that belongs to the externaltorsional resistance expected region 24 in the medial midfoot region 20.

Further, the external torsional resistance expected region 24 may bedefined to be formed of the first region 26, the second region 28, and athird region 30 surrounded by the line s, the line u, the line x, andthe line w in planar view. It is considered that by providing therigidity lowering portion 32 in the foregoing external torsionalresistance expected region 24, the external torsional resistance of thesole midfoot portion 14 can be effectively reduced when a largerexternal torsional load is applied to the sole 10.

This rigidity lowering portion 32 is also preferably provided in parts(the range S1, the range S2, and the part indicated by a range S3) thatbelong to the external torsional resistance expected region 24 outsidethe medial midfoot region 20, other than the part that belongs to theexternal torsional resistance expected region 24 in the medial midfootregion 20.

Next, the effects of the invention based on the presence or absence ofthe above-described conditions will be explained using analysis. FIG. 11shows a sole 100 of a reference example used for the analysis. The sole10 according to an exemplary embodiment is shown in FIG. 7. Thedimensional conditions and physical conditions of the soles 10 and 100were set to be the same as those in the analysis of FIG. 8.

In each of the sole 100 according to the reference example and the sole10 according to the exemplary embodiment, a transverse groove portion 40is provided at a part corresponding to the MP joint in the forefootportion 12 of the sole such that the sole is bent at the forefootportion 12 of the sole around the foot width direction axis during astanding on tiptoe posture. In the sole 10 according to the exemplaryembodiment, two medial transverse groove portions 34 are provided asrigidity lowering portions 32 that lower the bending rigidity of themedial midfoot region 20. Further, in the sole 10 according to theexemplary embodiment, one more medial transverse groove portion 34 isprovided as a rigidity lowering portion 32 that lowers the bendingrigidity of the external torsional resistance expected region 24 in thepart S1 located outside the range of the medial midfoot region 20. Thethree medial transverse groove portions 34 extend in the foot widthdirection Y from the medial edge 10 c of the sole 10 and are provided atintervals in the foot longitudinal direction Lx. No similar rigiditylowering portion 32 is provided in the sole midfoot portion 14 accordingto the reference example.

The respective deformation characteristics of the soles 10 and 100 withrespect to external torsion were evaluated by eigenvalue analysis. Morespecifically, the respective torsional frequencies, which were therespective natural frequencies occurring when the characteristicvibration mode of the soles 10 and 100 was torsional vibration, wereobtained by the eigenvalue analysis, and the deformation characteristicsof the soles 10 and 100 were evaluated using the respective torsionalfrequencies. It means that the smaller the torsional frequencies become,the smaller the respective external torsional resistances of the soles10 and 100 become.

FIG. 12 is a graph showing the torsional frequencies obtained by thisanalysis. As shown in this figure, the torsional frequency of the sole10 according to the exemplary embodiment was smaller than that of thesole 100 according to the reference example. This indicates that thesole 10 according to the exemplary embodiment had smaller externaltorsional resistance than the sole 100 according to the referenceexample.

Next, the effects of the invention based on the presence or absence ofthe above-described conditions will be explained using an experimentexample. In this experiment, a sole whose size and physical propertiesas the same as those of the two types of soles shown in FIGS. 7 and 11was used. In this experiment, shoes using these soles were worn. Usingthese shoes, the wearer kept a posture for 40 seconds where the wearerfocused on keeping his/her body torso lifted from the ground contactsurface while having his/her elbows touching the ground and having therespective forefoot portions 12 of the soles touching the ground suchthat the body parts from the head to the heel became straight.

The result of this experiment was evaluated using the torsion angle ofthe sole midfoot portion 14 and the amount of the ankle unstableness ofthe wearer. Using a motion capture system, this torsion angle wasmeasured by acquiring three-dimensional positional information ofmarkers attached to a plurality of parts of the sole 10. This torsionangle is defined as the angle formed by the ground contact surface ofthe sole midfoot portion with respect to the ground contact surface ofthe sole rearfoot portion. In the same way as in the torsion angle, theamount of the ankle unstableness of the wearer was also measured byacquiring three-dimensional positional information of markers attachedto the ankle.

FIG. 13A shows the measurement result for torsion angles obtained by theexperiment, and FIG. 13B shows the measurement result for the amount ofthe ankle unstableness. As compared with the sole 100 according to thereference example, it can be confirmed that the sole 10 according to theexemplary embodiment had a larger torsion angle of the sole midfootportion 14. Based on this, it can be confirmed that the sole 10according to the exemplary embodiment had smaller external torsionalresistance than the sole 100 according to the reference example.Further, it can be confirmed that the sole 10 according to the exemplaryembodiment had a smaller amount of the ankle unstableness than the sole100 according to the reference example. Based on this, it can beconfirmed that good stability can be obtained during a take standing ontiptoe posture by the shoe using the sole 10 according to the example.This is considered to be due to the bony locking mechanism being able tobe induced in accordance with an increase in the torsion angle of thesole midfoot portion 14, as described above.

FIG. 14 is a bottom view showing a sole 10 according to a firstexemplary variation. Lateral transverse groove portions 44, which areopen on the ground contact surface 10 e of the sole 10 and extend fromthe lateral edge 10 d of the sole 10 in the foot width direction Y, areformed in the sole midfoot portion 14 and the rearfoot portion 16 of thesole 10 according to the first exemplary variation. In this case, thebending rigidity decreases in a range including a lateral midfoot region22 of the sole 10. In accordance with this, it is difficult to provide asufficient difference in bending rigidity between the medial midfootregion 20 and a lateral midfoot region 22 of the sole 10. In order tosufficiently obtain the effect of reducing the external torsionalresistance at the sole midfoot portion 14, this difference in thebending rigidity is preferably as large as possible.

Therefore, the lateral transverse groove portions 44 extending from thelateral edge 10 d of the sole 10 in the foot width direction Y arepreferably not formed in a partial range Sb of the sole 10 in the footlongitudinal direction X. The partial range Sb includes a range Sb1 inthe foot longitudinal direction X where all rigidity lowering portions32 are provided and all of a range Sb2 on the heel side of the rangeSb1. This allows a sufficient difference in bending rigidity to beprovided between the medial midfoot region 20 and the lateral midfootregion 22 of the sole 10, and the effect of reducing the externaltorsional resistance at the sole midfoot portion 14 can thus be moreeasily obtained. From the same point of view, it can be considered thatthe lateral transverse groove portions 44 are preferably not formed in arange Sc, which is located on the heel side of the line y describedabove.

First Embodiment

FIG. 15 is a side view of a shoe 52 using a shoe bottom 50 according toa first embodiment as viewed from the medial side in the foot widthdirection. The shoe 52 is used, for example, for exercise in a room suchas a gym; however, the usage thereof is not particularly limited. Theshoe 52 includes a shoe bottom 50, which supports the wearer's foot, andan upper 54, which covers the wearer's foot.

The shoe bottom 50 includes a sole 10. The sole 10 according to thepresent embodiment includes a midsole 56. The sole 10 has a groundcontact surface 10 e, which comes into contact with the road surface.The ground contact surface 10 e according to the present embodiment isformed by the lower surface of the midsole 56. The midsole 56 mainly hasa role of alleviating the impact of landing. The midsole 56 is formedusing, for example, a foam or non-foam resin, or the like.

FIG. 16 is a bottom view of the sole 10. A plurality of medialtransverse groove portions 34 are formed on the sole 10. The pluralityof medial transverse groove portions 34 are formed so as to be open onthe ground contact surface 10 e of the sole 10 and to extend in thein-plane direction of the ground contact surface 10 e. The plurality ofmedial transverse groove portions 34 extend in the foot width directionY from the medial edge 10 c of the sole 10 toward the lateral edge 10 d.The plurality of medial transverse groove portions 34 are provided atintervals in the leg longitudinal direction Lx. The respective endportions of the plurality of medial transverse groove portions 34 on thelateral side in the foot width direction Y are provided at intermediatepositions in the foot width direction Y of the sole 10.

The extending direction of the medial transverse groove portions 34 isset to be a direction oblique to the foot width direction axis. Morespecifically, the extending direction is set to be a direction that isthe same as the direction along a line t in the planar view. As shown inFIG. 2, this direction along the line t is a direction that is the sameas the direction along a straight line Ld connecting the rear endportion of the first metatarsal bone Bf1 to the rear end portion of thefifth metatarsal bone Bf5 constituting the Lisfranc joint Jb. Theexpression “the same” includes not only the case where the directionsare the same as interpreted literally but also the case where thedirections are almost the same. When this condition is satisfied, theheel side end portion of the sole 10 easily turns in the supinationdirection, and as a result, the sole midfoot portion 14 can be easilytwisted outward.

The depth of the medial transverse groove portions 34 from the groundcontact surface 10 e is preferably as deep as possible from theviewpoint of effectively reducing the bending rigidity of the medialmidfoot region 20 of the sole 10. From this viewpoint, the depth of themedial transverse groove portions 34 is preferably 1% or more, morepreferably 5% or more, and particularly preferably 10% or more, withrespect to the average thickness of the entire sole 10.

The groove width of the medial transverse groove portions 34 ispreferably 1 mm or more. The groove width means the opening width of themedial transverse groove portions 34 at the ground contact surface 10 eof the sole 10. The groove width is set to 1 mm or more in order toeffectively reduce the bending rigidity of the medial midfoot region 20of the sole 10. Although the upper limit value of the groove width isnot particularly limited, the groove width is preferably, for example,20 mm or less.

An example is shown in which the shape of the medial transverse grooveportions 34 is a straight line shape extending in the in-planedirection; however, the shape is not limited thereto. For example, acurved shape extending in the in-plane direction or a shape such as acombination of a straight line and a curved line may be employed.

Each of the plurality of medial transverse groove portions 34constitutes a rigidity lowering portion 32, which lowers the bendingrigidity of the medial midfoot region 20. A plurality of rigiditylowering portions 32 are thus provided. One medial transverse grooveportion 34, which is a part of the plurality of medial transverse grooveportions 34, is formed so as to extend from the medial midfoot region 20to the lateral midfoot region 22. As described above, the rigiditylowering portions 32 are assumed to be provided in the medial midfootregion 20; however, the rigidity lowering portions 32 may be providedsuch that a portion of the rigidity lowering portions 32 extends overthe lateral midfoot region 22. Further, the plurality of rigiditylowering portions 32 are formed so as to be located on the first region26, the second region 28, and the third region 30 of the externaltorsional resistance expected region 24, respectively. Even when therigidity lowering portions 32 are provided in the external torsionalresistance expected region 24 as described above, the rigidity loweringportions 32 may be provided so as to extend outside the externaltorsional resistance expected region 24.

Second Embodiment

FIG. 17 is a bottom view showing a sole 10 according to a secondembodiment. FIG. 18A is a side view of the sole 10 viewed from themedial side in the foot width direction, and FIG. 18B is a side view ofthe sole 10 viewed from the lateral side in the foot width direction.

The sole 10 according to the second embodiment has a longitudinal grooveportion 36 extending in the foot longitudinal direction X in addition toa plurality of medial transverse groove portions 34. The longitudinalgroove portion 36 is open on the ground contact surface 10 e of the sole10. The longitudinal groove portion 36 is connected to the end portionon the lateral side in the foot width direction of each of the pluralityof medial transverse groove portions 34. The longitudinal groove portion36 according to the present embodiment is provided so as to fit in amedial midfoot region 20 and is not provided in a lateral midfoot region22.

The longitudinal groove portion 36 according to the present embodimenthas a heel side portion 36 b provided on the heel side of anintermediate portion 36 a in the foot longitudinal direction X thereofand a toe side portion 36 c provided on the toe side of the intermediateportion 36 b. The intermediate portion 36 a of the longitudinal grooveportion 36 according to the present embodiment is provided so as to forma convex shape toward the lateral side in the foot width direction. Theheel side portion 36 b is provided being inclined with respect to thefoot longitudinal axis so as to become closer to the medial edge 10 c ofthe sole 10 toward the heel side of the sole 10. The distal end portionof the heel side portion 36 b connects with the medial edge 10 c of thesole 10. The toe side portion 36 c is provided being inclined withrespect to the foot longitudinal axis so as to become closer to themedial edge 10 c of the sole 10 toward the toe side of the sole 10. Thedistal end portion of the toe side portion 36 c connects with the medialedge 10 c of the sole 10. The longitudinal groove portion 36 is providedsuch that a part of the range thereof that extends from the intermediateportion 36 a to the heel side overlaps with a line u.

A plurality of island-like regions 38 surrounded by the plurality ofmedial transverse groove portions 34, the longitudinal groove portion36, and the medial edge 10 c of the sole 10 are formed in the medialmidfoot region 20 of the sole 10. The island-like regions 38 areseparated from the other region including the lateral midfoot region 22of the sole 10 by a groove portion including the longitudinal grooveportion 36. The “groove portion including the longitudinal grooveportion 36” in the present embodiment refers to only the longitudinalgroove portion 36. If the longitudinal groove portion 36 does notconnect with the medial edge 10 c of the sole 10, the medial transversegroove portion 34 closest to the toes or the heel is also included. Itcan be considered that the island-like regions 38 are separated from theregion including the lateral midfoot region 22 by the groove portionincluding the longitudinal groove portion described above.

Thereby, when the medial midfoot region 20 is attempted to be bent anddeformed at a part where the plurality of medial transverse grooveportions 34 are formed, the deformation of the plurality of medialtransverse groove portions 34 is prevented from influencing the lateralmidfoot region 22 side of the longitudinal groove portion 36. Therefore,it becomes easier to design such that the bending rigidity of the medialmidfoot region 20 and the bending rigidity of the lateral midfoot region22 are different from each other.

The groove width of the longitudinal groove portion 36 is set to belarger than the respective groove widths of the medial transverse grooveportions 34. The medial transverse groove portion 34 that connects withthe end portion of the longitudinal groove portion 36 and is the closestto the toes is also set to be larger than the respective groove widthsof the other medial transverse groove portions 34.

A plurality of second transverse groove portions 42 are formed in aforefoot portion 12 and a midfoot portion 14 of the sole 10 according tothe second embodiment. The plurality of second transverse grooveportions 42 are provided at intervals in the leg longitudinal directionLx. Some second transverse groove portions 42 of the plurality of secondtransverse groove portions 42 are provided so as to reach the medialedge 10 c from the lateral edge 10 d of the sole 10. The other secondtransverse groove portions 42 of the plurality of second transversegroove portions 42 are provided so as to extend toward the medial edge10 c from the lateral edge 10 d of the sole 10. The respective endportions of the other second transverse groove portions 42 are providedat intermediate positions in the foot width direction of the sole 10.Any of the second transverse groove portions 42 is provided on the toeside of the above-described line y.

FIG. 19A is a bottom view of a sole 10 according to a second exemplaryvariation. FIG. 19B is a bottom view of a sole 10 according to a thirdexemplary variation. FIG. 19C is a bottom view of a sole 10 according toa fourth exemplary variation. Regarding the longitudinal groove portion36 in the example of FIG. 17, an example has been explained where bothend portions of the longitudinal groove portion 36 connect with themedial edge 10 c of the sole 10. Both end portions of the longitudinalgroove portion 36 according to the present example are provided atlocations away from the medial edge 10 c of the sole 10 in the footwidth direction. In the longitudinal groove portion 36 according to thepresent example, the end portions of the medial transverse grooveportions 34 and the end portions of the longitudinal groove portion 36are connected so as to form corner portions with the medial transversegroove portions 34. In addition to this, the end portions of thelongitudinal groove portion 36 may be provided so as to end withoutconnecting with other groove portions.

FIG. 19A shows an example where a single longitudinal groove portion 36is provided, and FIG. 19B shows an example where a plurality oflongitudinal groove portions 36-A and 36-B (hereinafter, genericallyreferred to as longitudinal groove portions 36). The plurality oflongitudinal groove portions 36-A and 36-B include a first longitudinalgroove portion 36-A on the lateral side in the foot width direction anda second longitudinal groove portion 36-B on the medial side in the footwidth direction. The first longitudinal groove portion 36-A is providedso as to connect with end portions of the plurality of medial transversegroove portions 34. The second longitudinal groove portion 36-B isprovided so as to connect with intermediate portions of the plurality ofmedial transverse groove portions 34 such that the second longitudinalgroove portion 36-B intersect with the intermediate portions in aT-shape or X-shape.

FIGS. 19A and 19B show examples where the respective longitudinal grooveportions 36 are provided so as to extend in a linear manner along therespective lines s, and in FIG. 19C shows an example where thelongitudinal groove portion 36 is provided so as to extend in a linearmanner along the line u. The expression “linear” means a shape lookinglike a straight line and does not mean a strictly linear shape in ageometrical manner. An extending direction Pb in which the linearlongitudinal groove portion 36 extends from the toe side to the heelside as described above is set to have, for example, an angle formed bythe direction axis thereof with respect to the line s of from 0 to 15degrees.

Third Embodiment

FIG. 20 is a side view of a shoe bottom 50 according to a thirdembodiment as viewed from the same viewpoint as that of FIG. 15. In theabove-described embodiment, an example has been explained where a sole10 has only a midsole 56; however, the sole 10 may have an outer sole 58as well.

The outer sole 58 is disposed below the midsole 56 and is attached tothe lower surface of the midsole 56 by adhesion or the like. The groundcontact surface 10 e of the sole 10 is formed by the lower surface ofthe outer sole 58. The outer sole 58 mainly has a role of securing gripperformance against the road surface. The outer sole 58 is formed using,for example, a non-foam or foam rubber, or the like. The midsole 56 isformed to be thicker than the outer sole 58 from the viewpoint ofplaying the role of alleviating the impact of the landing. Further,since the outer sole 58 plays a role of securing the grip performance,the outer sole 58 may have hardness that is larger than that of themidsole 56. The medial transverse groove portions 34 according to thepresent embodiment are formed within a range that does not reach themidsole 56 from the ground contact surface 10 e of the outer sole 58.

Fourth Embodiment

FIG. 21 is a side view of a shoe bottom 50 according to a fourthembodiment as viewed from the same viewpoint as that of FIG. 15.Different from the example of FIG. 20, medial transverse groove portions34 according to the present example are formed within a range thatreaches a midsole 56 from the ground contact surface 10 e of an outersole 58.

As described, a sole 10 may have either one or both of the midsole 56and the outer sole 58. For example, although not shown in the figure,the sole 10 may have only the outer sole 58.

Described above is a detailed explanation of the embodiments of thepresent invention. All of the above-described embodiments merely showspecific examples for carrying out the present invention. The details ofthe embodiments do not limit the technical scope of the presentinvention, and many design changes such as change, addition, deletion,etc., of constituent elements may be made without departing from thespirit of the invention as defined by the claims. In the above-describedembodiments, such details that are changeable in a design manner areexplained with notations of “according to the embodiment”, “in theembodiment”, etc.; however, it does not mean that design changes are notallowed for features without such notations. Further, hatching appliedto cross sections of the drawings does not limit the material of anobject with the hatching.

The expression “foot longitudinal direction Lx” may be defined as adirection along a straight line connecting the toe side end portion ofthe second toe to the rearmost end portion (calcaneus tuberosity) of thecalcaneus of the wearer's foot, which is assumed to be on the sole 10 bydesign.

As the sole center line s, a straight line extending along the footlongitudinal direction Y, which divides the full width Lb of the sole 10into 1:1, may be used. From another viewpoint, a straight line along thefoot longitudinal direction Y may be used by which the full width Lb ofthe sole 10 is divided from 1:1 to 3.7:3.2 from the medial side in thefoot width direction to the lateral side in the foot width direction.

For example, the midsole 56 may be formed by stacking two or more partshaving different material properties in the vertical direction orarranging the parts in the foot longitudinal direction.

DESCRIPTION OF THE REFERENCE NUMERALS

10 sole, 10 c medial edge, 10 d lateral edge, 10 e ground contactsurface, 14 midfoot portion, 16 rearfoot portion, 16 a toe side endportion, 16 b heel side end portion, 16 c continuous surface, 20 medialmidfoot region, 22 lateral midfoot region, 24 external torsionalresistance expected region, 26 first region, 28 second region, 30 thirdregion, 32 rigidity lowering portion, 34 medial transverse grooveportion, 36 longitudinal groove portion, 44 lateral transverse grooveportion, 50 shoe bottom, 52 shoe, 56 midsole, 58 outer sole

INDUSTRIAL APPLICABILITY

The present invention relates to shoe bottoms of shoes.

1. A shoe bottom comprising a sole, wherein when a midfoot portion of the sole is divided by a predetermined sole center line into a medial midfoot region and a lateral midfoot region one on each side in the foot width direction, the sole has a rigidity lowering portion that is provided in the medial midfoot region, and wherein, in such a manner that the bending rigidity of the medial midfoot region around a foot width direction axis becomes smaller than that of the lateral midfoot region, the rigidity lowering portion in the medial midfoot region reduces the bending rigidity of the medial midfoot region due to another factor other than the shape of a medial edge and the shape of a lateral edge of the sole in a planar view.
 2. The shoe bottom according to claim 1, wherein a continuous surface that is continuous in the foot longitudinal direction from a toe side end portion to a heel side end portion of a rearfoot portion of the sole is formed on a ground contact surface of the sole.
 3. The shoe bottom according to claim 1, wherein a lateral transverse groove portion that is open on the ground contact surface of the sole and that extends from the lateral edge in the foot width direction is not formed in a range in the foot longitudinal direction where the rigidity lowering portion is provided and in a range in the foot longitudinal direction located on the heel side of the range.
 4. The shoe bottom according to claim 1, wherein the rigidity lowering portion is open on the ground contact surface of the sole and serves as a medial transverse groove portion that extends in the foot width direction from the medial edge.
 5. The shoe bottom according to claim 1, wherein the sole has either one or both of a midsole and an outer sole, and wherein a reinforcing member is not attached to the midfoot portion of the sole.
 6. The shoe bottom according to claim 1, wherein on the sole, a plurality of medial transverse groove portions are formed that are open on a ground contact surface of the sole and extend in the foot width direction from the medial edge, and a longitudinal groove portion is formed that is open on the ground contact surface of the sole, extends in the foot longitudinal direction, and connects with respective end portions of the plurality of medial transverse groove portions in the foot width direction.
 7. The shoe bottom according to claim 1, wherein in a planar view of the sole, given that straight lines along the foot width direction that divide the full length La of the sole in the foot longitudinal direction into 1.5:1.0:1.1 from the toe side to the heel side are defined as lines p and q, respectively, a straight line along the foot longitudinal direction that divides the full width Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width direction is defined as a line s, which serves as the sole center line, being viewed from a point O1, which is the intersection point of the line p and the line s, a straight line obtained by rotating the line p by 13 degrees around the point O1 in an outward direction that rotates the toe side outward in the foot width direction, is defined as a line t, a straight line obtained by rotating the line s by 8 degrees around the point O1 in the outward direction viewed from the point O1 is defined as a line u, being viewed from a point O2, which is the intersection point of the line u and the line q, a straight line obtained by rotating the line q by 5 degrees around the point O2 in the outward direction is defined as a line v, a region surrounded by the line t, the line u, the line v, and the medial edge is defined as a first region, and a region formed of the first region is defined as an external torsional resistance expected region, a rigidity lowering portion is provided in the external torsional resistance expected region.
 8. The shoe bottom according to claim 1, wherein in a planar view of the sole, given that straight lines along the foot width direction that divide the full length La of the sole in the foot longitudinal direction into 1.5:1.0:0.2:0.9 from the toe side to the heel side are defined as lines p, q, and r, respectively, a straight line along the foot longitudinal direction that divides the full width Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width direction is defined as a line s, which serves as the sole center line, being viewed from a point O1, which is the intersection point of the line p and the line s, a straight line obtained by rotating the line p by 13 degrees around the point O1 in an outward direction that rotates the toe side outward in the foot width direction, is defined as a line t, a straight line obtained by rotating the line s by 8 degrees around the point O1 in the outward direction viewed from the point O1 is defined as a line u, being viewed from a point O2, which is the intersection point of the line u and the line q, a straight line obtained by rotating the line q by 5 degrees around the point O2 in the outward direction is defined as a line v, being viewed from a point P, which is the intersection point of the line r and the line u, a straight line obtained by rotating the line r by 4 degrees around the point P in the outward direction is defined as a line w, a straight line connecting a point O5, which is the intersection point of the medial edge and the line w, and the point O2 is defined as a line x, a region surrounded by the line t, the line u, the line v, and the medial edge is defined as a first region, a region surrounded by the line v, the line x, and the medial edge is defined as a second region, and a region formed of the first region and the second region is defined as an external torsional resistance expected region, a rigidity lowering portion is provided in the external torsional resistance expected region.
 9. The shoe bottom according to claim 1, wherein in a planar view of the sole, given that straight lines along the foot width direction that divide the full length La of the sole in the foot longitudinal direction into 1.5:1.0:0.2:0.9 from the toe side to the heel side are defined as lines p, q, and r, respectively, a straight line along the foot longitudinal direction that divides the full width Lb of the sole into 1.2:1.0 from the medial side to the lateral side in the foot width direction is defined as a line s, which serves as the sole center line, being viewed from a point O1, which is the intersection point of the line p and the line s, a straight line obtained by rotating the line p by 13 degrees around the point O1 in an outward direction that rotates the toe side outward in the foot width direction, is defined as a line t, a straight line obtained by rotating the line s by 8 degrees around the point O1 in the outward direction viewed from the point O1 is defined as a line u, being viewed from a point O2, which is the intersection point of the line u and the line q, a straight line obtained by rotating the line q by 5 degrees around the point O2 in the outward direction is defined as a line v, being viewed from a point P, which is the intersection point of the line r and the line u, a straight line obtained by rotating the line r by 4 degrees around the point P in the outward direction is defined as a line w, a straight line connecting a point O5, which is the intersection point of the medial edge and the line w, and the point O2 is defined as a line x, a region surrounded by the line t, the line u, the line v, and the medial edge is defined as a first region, a region surrounded by the line v, the line x, and the medial edge is defined as a second region, a region surrounded by the line s, the line u, the line x, and the line w is defined as a third region, and a region formed of the first region, the second region, and the third region is defined as an external torsional resistance expected region, a rigidity lowering portion is provided in the external torsional resistance expected region.
 10. The shoe bottom according to claim 1, wherein the factor is any one or a combination of two of a recessed portion that is open on the ground contact surface of the sole and the elongation characteristic of a material constituting the sole.
 11. A shoe comprising the shoe bottom according to claim
 1. 